Med9 Is a Novel eIF4E-Interacting Protein in Saccharomyces cerevisiae

Area of Science:

• Molecular Biology
• Biochemistry
• Yeast Genetics

Background:

• The cap-binding protein eukaryotic initiation factor 4E (eIF4E) is crucial for mRNA metabolism and translation.
• eIF4E's biological functions are determined by its interaction partners.
• Its best-characterized role involves promoting mRNA translation via interaction with eIF4G.

Purpose of the Study:

• To identify novel interaction partners of eIF4E in the yeast *Saccharomyces cerevisiae*.
• To characterize the interaction between eIF4E and newly identified partners.

Main Methods:

• Genomic yeast two-hybrid screen using eIF4E as bait.
• Confirmation of physical interaction using recombinant proteins and co-immunoprecipitation.
• Site-directed mutagenesis to identify key amino acids in the interaction.

Main Results:

• Med9, a component of the RNA polymerase II Mediator complex, was identified as a novel eIF4E interactor.
• The eIF4E-Med9 interaction was confirmed both in vitro and in vivo.
• A W75A mutation in eIF4E, which disrupts interactions with known partners, had minimal effect on Med9 binding.
• Mutagenesis of Med9 identified specific amino acids (F65, I66, H68) crucial for eIF4E recognition.

Conclusions:

• eIF4E interacts with Med9, a component of the RNA polymerase II Mediator complex.
• This interaction is distinct from other known eIF4E interactions and may occur in both cellular compartments.
• The findings expand the known interactome of eIF4E and suggest a role in nuclear processes.